The present invention broadly relates to yarn or thread-break monitors and, more specifically, pertains to a new and improved construction of a needle thread-break monitor or stop motion for embroidery machines.
Generally speaking, the needle yarn or thread-break monitor or stop motion of the present invention is intended for use in embroidery machines and is of the type comprising a two-armed or double-armed pivot lever or rocker or rocking lever acting as a switch in an electrical or current circuit of an alarm system and being mounted on a bearing or support shaft forming one pole of the switch. The rocker or rocking lever is pivotable through an angle limited by stop or abutment means between a closed position and an open position of the switch. The stop or abutment means limiting the closed position of the switch forms the second pole or terminal of the switch. The rocker or pivot lever is held in the open position of the switch by a tensioned needle thread guided in a thread guide on the rocker lever.
Needle thread-break monitors or stop motions of this type are particularly employed in embroidery machines provided with a plurality of needles and serve to generate an electrical signal when a needle thread or yarn breaks, which signal may be an alarm signal or may serve to shut down the corresponding machinery.
A known needle thread-break monitor or stop motion is employed for this purpose in which a bearing shaft forming one pole or terminal of the electrical circuit is supported on a mounting rail or support forming the other pole or terminal of the switch through insulating means. Normally, such a bearing shaft is provided with a plurality of such switches in parallel. When a needle thread breaks, the corresponding rocking lever drops with its thread guide-carrying arm onto a contact edge of the mounting rail or support and closes the alarm circuit. An insulating sleeve is fitted to the contact arm of the rocking lever carrying the thread guide for rendering selected needle thread monitors inoperative. These insulating sleeves can be manually shifted into a contact-inhibiting position. The individual continuously tensioned needle threads are drawn from a thread supply and guided over a braking drum. A thread lifting or pick-up tube is arranged between the braking drum and the needle thread monitor mechanism to hold the needle threads up. This lifting tube simultaneously serves as a conduit for guiding the electrical conductors or lines to the bearing shaft and to the mounting rail or support.
Needle thread-break monitors of this known type have a number of considerable disadvantages. For instance, such needle thread-break monitors or stop motions have proven to be unusable for embroidering goods with metallized yarns, since this electrically conductive yarn short-circuits the electrical circuit of the alarm system if it touches the mounting rail or support forming one pole or terminal of the switch. Such contacts take place constantly due to yarn vibration.
The insulating sleeve mounted on the contact arm of the rocking lever for enabling or inhibiting electrical contact of the needle thread-break monitor or stop motion is unsatisfactory with respect to manipulation and security. Furthermore, a failure of the alarm system can arise when a shuttle thread breaks and a needle thread is not tightened by the thread supply and adheres to the braking drum and is held high enough by the thread lifting or pick-up tube that the rocking lever does not drop onto the mounting rail. Finally, in large embroidery machines having a plurality of switches next to one another, the rocking levers, which are not laterally guided on the bearing shaft, can migrate along the bearing shaft, which may lead to a diagonal or inclined feed of the embroidery threads.